(Not Applicable)
(Not Applicable)
1. Technical Field
This invention relates to the field of electronic article surveillance (EAS), and more particularly to an antenna adapted for activation and deactivation of EAS markers.
2. Description of the Related Art
Electronic article surveillance (EAS) systems for detecting the unauthorized removal of articles or goods from retail establishments or other facilities are well known and widely used. In general, EAS systems employ a marker secured to an article or item. The marker contains an active element and a bias element. When the bias element is magnetized, or activated, it applies a bias magnetic field to the active element, which causes the active element to be mechanically resonant at a predetermined frequency upon exposure to an interrogation signal, which alternates at the predetermined frequency. The interrogation signal can be generated by detecting apparatus, which can also detect the resonance of the marker, the resonance having been induced by the interrogation signal. Specifically, a transmitter can emit a signal at a defined frequency to the receiver, the area between the transmitter and receiver defining a surveillance area. When the marker encroaches upon the surveillance area, the active element in the marker distorts the transmitted signal, alerting the receiver of the presence of the marker. In response, the receiver can activate an alarm.
The marker can be deactivated or removed by authorized personnel from any article or good authorized to be removed from the premises, thereby permitting passage of the article or good through the surveillance area without triggering an alarm activation. When the marker is deactivated by demagnetizing its active element, the marker can no longer produce the detectable tag signal. Such deactivation of the marker, can occur, for example, when an employee of a retail establishment passes an EAS tagged article over a deactivation device at a checkout counter thereby deactivating the marker. The EAS marker can be deactivated by exposing the bias element to an alternating magnetic field of sufficient magnitude to degauss the bias element. After the bias element is degaussed, the marker""s resonant frequency is substantially shifted from the predetermined frequency, and the marker""s response to the interrogation signal is at too low an amplitude for detection by the detecting apparatus. Generally, marker activation and deactivation devices include a coil structure energizable to generate a magnetic field of character and magnitude sufficient to render the marker either active or inactive. One known type of marker activation and deactivation device includes one or more coils energized by a current signal to generate the necessary magnetic field.
Activation and deactivation of a marker requires the use of a steady state or time varying magnetic field of a specific intensity. Current antennas used to generate the required magnetic field can generate far magnetic fields capable of interfering with proximate electronic equipment. Thus, items present in retail stores could be adversely affected by exposure to the magnetic field generated by a marker deactivation device. Presently, significant time and expense are required to ameliorate the effects of marker activation and deactivation on proximate electronic equipment. For instance, current amelioration techniques include increasing the physical space between the activation and deactivation antenna and other electronic equipment, shielding the antenna, the affected electronic equipment, or both, and redesigning the affected electronic equipment. Yet, current measures to reduce the interference can add cost to the retail checkout environment. Moreover, the same current measures can degrade the ergonomics of the retail check stand. Consequently, no present solution exists for limiting the far field transmission of a signal while enhancing the strength of a near field signal. Hence, a present need exists for an EAS marker activation/deactivation antenna providing an adequate magnetic field to activate and deactivate an EAS marker in the near field while simultaneously reducing the far field produced to limit interference.
An EAS marker antenna in accordance with the inventive arrangement provides an adequate magnetic field to activate/deactivate an EAS marker in the near field while simultaneously reducing the far field produced to limit interference. In particular, the present invention includes an arrangement of antenna coils and cores capable of providing an adequate magnetic field to activate or deactivate acoustomagnetic and electromagnetic markers in the near field while simultaneously reducing the far magnetic field. Thus, in limiting electromagnetic interference caused by an EAS marker activation/deactivation antenna, the inventive arrangement has advantages over all current amelioration techniques, and provides an inventive apparatus and method for ameliorating far field interference caused by the activation and deactivation of an EAS marker.
An EAS activation/deactivation antenna in accordance with the inventive arrangements comprises a core; a coil arrangement having at least two coils spirally wrapped about the core, the first coil having a first rotational direction and the second coil having a rotational direction counter to the first rotational direction; and, a current source operatively connected to the coil arrangement. In consequence of the inventive arrangement, a current supplied by the current source can excite the coil arrangement to produce a significant near magnetic field and a reduced far magnetic field.
In one embodiment, the core can be a rectangular core. Furthermore, the core can be formed of powdered iron, or other suitable material. Also, the coil arrangement can comprise a single wire forming two coils spirally wrapped about the core, the first coil having a first rotational direction and the second coil having a rotational direction counter to the first rotational direction. Alternatively, the coil arrangement can comprise a first wire forming two coils spirally wrapped about an y-axis of the core, the first coil having a first rotational direction and the second coil having a rotational direction counter to the first rotational direction; and, a second wire forming two coils spirally wrapped about an x-axis of the core, the first coil having a first rotational direction and the second coil having a rotational direction counter to the first rotational direction.
A method for simultaneously limiting a far magnetic field and enhancing a near magnetic field in an EAS marker activation/deactivation antenna comprises the steps of: first spirally wrapping a first coil about an axis of a core in a first rotational direction; second spirally wrapping a second coil about the axis of the core in a rotational direction counter to the first rotational direction; combining the first and second coils to form a coil arrangement; and, supplying a current to the coil arrangement, wherein the current can excite the coil arrangement to produce a significant near magnetic field and a reduced far magnetic field. In addition, the inventive method can comprise the steps of: third spirally wrapping a third coil about a second axis of the core in a third rotational direction; fourth spirally wrapping a fourth coil about the second axis of the core in a rotational direction counter to the third rotational direction; and, adding the third and fourth coil to the coil arrangement. Finally, the method can include placing an EAS marker in the near magnetic field of the EAS marker activation/deactivation antenna during the supplying step, wherein the supplying step can activate or deactivate the EAS marker while producing a reduced far magnetic field.
Alternatively, a method for simultaneously limiting a far magnetic field and enhancing a near magnetic field in an EAS marker activation/deactivation antenna comprises the steps of: spirally wrapping a wire about an axis of a core in a first rotational direction; reversing the first rotational direction and spirally wrapping the wire about the axis of the core in a rotational direction counter to the first rotational direction; and, supplying a current to the wire, wherein the current can excite the wire to produce a significant near magnetic field and a reduced far magnetic field. In addition, the inventive method can comprise the steps of: spirally wrapping a second wire about a second axis of the core in a second rotational direction; reversing the second rotational direction and spirally wrapping the second wire about the second axis of the core in a rotational direction counter to the second rotational direction; and, supplying the current to the second wire.
The above-described embodiments can be driven by a decaying, alternating (AC) current to produce a decaying, alternating (AC) magnetic field for deactivation of EAS markers. Deactivation can also be accomplished by supplying a steady-state alternating current to produce a steady-state alternating magnetic field, with the required decay resulting from movement of the EAS marker from the field. The above-described embodiments can be driven by a direct current (DC) pulse to produce a direct current (DC) magnetic field pulse for activation of EAS markers. Activation can also be accomplished by supplying a steady state DC current to produce a DC steady state magnetic field.